1. Field of the Invention
This invention relates to meter yokes and meter boxes. More particularly, this invention relates to an expansion mechanism for mounting fluid meters in meter boxes and meter yokes.
2. Description of Related Art
In known handwheel expansion mechanisms for meter boxes or meter yokes, the handwheel part of the mechanism has a tendency to walk or move in the meter box or meter yoke assembly. In the art, "walking" is caused by relative movement that can take place between the inner and outer members of the handwheel assembly. All prior art known to the present inventor has the problem of "walking".
For example, in U.S. Pat. No. 5,003,821, a two-piece handwheel is disclosed. In this patent, a cup completely covers an O-ring in an O-ring groove provided in the sleeve. The handwheel and cup are integrally formed as a one-piece assembly. Walking occurs between the end of the extension cup of the handwheel assembly and the rubber seal of the meter box or meter yoke during installation of the handwheel. Rotation of the extension cup and the handwheel together causes the end of the extension cup to move (walk) upward on the flat rubber seal. Misalignment between the flow way of the expansion mechanism and the bore of the sealing gasket centered with the flow way of a meter valve or fitting is caused by `walking`.
FIGS. 5 and 6 illustrate another prior art design. FIG. 5 depicts the assembled design while FIG. 6 shows an exploded view of the prior art model. Handwheel assembly 100 includes body 102, handwheel 104, gasket/O-ring 106 and extension cup 108. Gasket or O-ring 106 is provided at the base of extension cup 108. Thus, there is no metal-on-metal contact between the handwheel body 104 and the extension cup 108. Rather, there is a metal-on-rubber-on metal contact between handwheel body 104, O-ring 106 and extension cup 108. When the gasket or ring seal is compressed, the fluid pressure will be transmitted by means of the compressed gasket to the lower end of the inner member to cause relative movement with respect to the handwheel. That is, the handwheel assembly tends to be pushed radially when the extension cup has its distal surface pressed in place. It is believed that the walking is caused by gasket 106, which under load, tends to act as a coupling between the end piece 108 and handwheel 104 under installation loading. Friction between the rubber gasket and metal parts allows rotation of the end piece 108 on the sealing gasket and therefore ` walking`. Furthermore, because the gasket or O-ring is not completely contained at its outer diameter, it can creep outward and thus reduce the sealing force. Walking, which allows flow way misalignment, occurs with the handwheel expansion mechanism 10 in the expanded position, as arms 103a and 103b are rotated. The design depicted in FIG. 5 has a reduced flow diameter. For a 5/8 inch handwheel assembly, the flow diameter is 0.594 inches.